Biplane ultrasonic linear and curved linear arrays have been applied in medical diagnostic imaging for several years. A biplane transducer array has the advantage of scanning a subject in two planes without having to use separate transducer probes. Typically, the arrays are mounted on a cylindrical probe wherein the curved linear array is mounted around a partial circumference of the probe and the regular (or straight) linear array is mounted along the probes longitudinal axis adjacent to the curved linear array. Arrays such as these are often used for endorectal and endovaginal imaging because of their small size and the expanded image field of the curved array.
The problem is that the scans of the two arrays in the transducer are originated from separate locations on the probe. Accordingly, to achieve two-dimensional images either the arrays or the object being scanned must be moved. This results in a loss of reference, a reduction of the accuracy of the measurements and decreased diagnostic ability.
U.S. Pat. No. 4,870,867 to Shaulov discloses an ultrasonic transducer which permits linear scanning along two intersecting planes. The two intersecting linear arrays are formed by partially dicing the opposite faces of a cross shaped transducer plate. Therefore, the transducer element electrodes for one of the arrays are formed on one side of the transducer plate and the electrodes for the other array are formed on the opposite side of the transducer plate.
The configuration disclosed in the Shaulov patent presents several drawbacks. First, capacitive coupling between the body and the non-grounded electrode create excessive noise in the image. Accordingly, the image produced by one of the two linear arrays is necessarily more noisy than the image produced by the other since the electrodes for the two arrays are formed on opposite sides of the transducer. Second, the array cannot be curved since the intersecting area between the two linear arrays has elements cut in orthogonal relation. Third, the array would have to be so small to fit onto an endorectal or endovaginal probe as to make the array non-functional.